Impairment of Real Estate and Impairment of Unconsolidated Entities (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	$ 425,463,000	$ 966,000	$ 425,463,000	$ 130,795,000
Westchester's Ridge Hill [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	372,587,000	0	372,587,000	0
Avenue at Tower City Center [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	0	0	0	72,473,000
Illinois Science and Technology Park [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	26,246,000	0	26,246,000	0
Terminal Tower [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	0	0	0	42,208,000
Post Office Plaza [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	0	0	0	14,378,000
Land inventory [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	16,307,000	0	16,307,000	0
Other [Member]
Schedule of Impairment of Real Estate Included in Continuing Operations [Line Items]
Impairment of Real Estate	$ 10,323,000	$ 966,000	$ 10,323,000	$ 1,736,000